Hi Tom,
Welcome to the API forum and thanks for your question! You’ve found an area of our naming behind the scenes that needs some work. To answer your question, setting ec_status to "EC Services" is the right way to get the Reverse Charge behaviour you want.
As we spoke about in a handling VAT after Brexit post, we recognise that this has the potential to be confusing, so there is work underway to separate out the Reverse Charge naming from our EC Status system. When that happens, we’ll publish an announcement here to give you time to migrate.
I hope that helps!
James
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Support Engineering Manager
FreeAgent UK